The codex is great. I like that they are elemental type "grim" (they all get stubborn, can't fall back on purpose), in an already grim world. I think the Deathwing and Ravenwing are great, and I think the respective knights are even cooler. (it gives you a reason to take non-troops) I love the Command Squads, and I love that they're the only thing that can take a banner, which makes them special (the 3 man ravenwing command squad, no option to enlarge, might have been a mistake, though).
The special characters are all cool as hell (eziekiel does indeed seem a little too cheap).
All the "new" units are just pants, though. (not counting the knights) Both flyers are too expensive with no real punch. The Land Speeder Vengence has hella punch, but c'mon, AV 10 and 2 hull points? It is going to be blown away so easily, it's ridiculous. The Darkshroud I could see being useful as mobile buff bubble....ravenwing knights have skilled rider so you could actually get them down to a 2++ cover on a turboboost move, whihc is pretty sweet. So that, at least, has value. But it's not for everybody.